Occasion sometimes arises to interdict the movement of vehicles in an outdoor area. This may be done by distributing mines, throughout the area, which function upon firing to disable a vehicle within an effective range from the mine. Mines are accordingly equipped with geophone apparatus for detecting the approach of targets within the range thereof.
It is desirable that such mines be not readily perceptible, and thus avoidable, by approaching vehicles: passive vehicle detecting arrangements are accordingly preferred. In this respect, seismic devices such as geophones, supported on or buried in the ground and responsive to vibrations in the earth caused by the vehicles, have been found quite satisfactory, as is taught in U.S. Pat. No. 4,468,763. A difficulty arises, however, since in such arrangements the seismic signal due to a light wheeled vehicle near to the geophone is not readily distinguishable from the seismic signal due to a heavy tracked vehicle more remote from the geophone. Some land mines are also known to be effective against light vehicles, such as jeeps, but to be relatively ineffective against heavier vehicles, such as armored tanks. It is inefficient to cause a mine to fire when its target is too remote for the mine to be effective, or when the target is one against which the mine is ineffective, since mines are expensive, high-technology devices.
Apparatus has been developed for receiving seismic vibrations from an approaching vehicle, distinguishing whether the seismic source is a heavy vehicle or a light vehicle, and giving a control signal if the source is a heavy vehicle. One arrangement for accomplishing this is taught in my co-pending patent application Ser. No. 753,733, filed July 10, 1985 and assigned to the assignee of the present application.